1. Field of the Invention
The invention relates to an ink let printer using a hot melt ink and, more particularly, to an ink jet printer which can inform the user of the molten state of the hot melt ink during the period of time while the hot melt ink is molten.
2. Description of Related Art
There exists an ink jet printer for printing characters, figures, etc. on a printing medium using an ink jet head and a hot melt ink, the ink being solid at ordinary temperature and melted by heat. This kind of ink jet printer includes an ink tank provided with a heater for heating the hot melt ink to melt the same so that it can be ejected onto the printing medium. The structure of such an ink tank provided with a heater is described with reference to FIG. 3. For FIG. 3, an ink tank 16 is provided at an upper portion in the ink jet printer 10. The ink tank 16 is provided with an ink supply opening 18 for supplying the hot melt ink in a solid state and a lid 20 for closing the ink supply opening 18. While the lid 20 is provided to prevent dust or the like from entering the ink tank 16 through the ink supply opening 18, the lid 20 is not tightly fitted to the ink supply opening 18.
When the lid 20 is tightly fitted to the ink supply opening 18, the following problems occur. Because the lid 20 closes the ink supply opening 18 of the ink tank 16, the lid 20 becomes very hot. Accordingly, when a user attempts to supply additional hot melt ink into the ink tank 16, it is very hard for the user to open the hot lid 20 that is tightly fitted to the ink supply opening 18. Further, the lid 20 is made of a resin and, as such, it is expanded by heat. Accordingly, when the lid 20 is tightly fitted to the ink supply opening 18 and is subsequently expanded by heat, the user cannot remove the lid 20 from the ink supply opening 18, and the user must delay the supply of the hot melt ink until the lid 20 cools to contract and restore an original shape. For these reasons, the lid 20 is not tightly fitted to the ink supply opening 18, but there is defined a small gap between the lid 20 and the ink supply opening 18 when the lid 20 is closed. Thus, the lid 20 can be easily removed from the ink supply opening 18.
When electric power is supplied, from a commercial power source, to the ink jet printer, the solid hot melt ink supplied through the ink supply opening 18 into the ink tank 16, is heated and melted by the heater and the ink is kept in a molten state. In printing, the molten ink in the ink tank 16 is used for printing on the printing medium using a printing mechanism. Thereafter, when the supply of electric power from the commercial power source to the ink jet printer is stopped, the heater is deenergized and stops heating the hot melt ink. Accordingly, the molten ink returns to a solid state as time passes.
However, if the ink jet printer is moved while the hot melt ink in the ink tank 16 is still in the molten state, after an interruption of the supply of the electric power from the commercial power source to the ink jet printer, there is a possibility that the molten ink in the ink tank 16 will spill from the small gap defined between the lid 20 and the ink supply opening 18. If the molten ink spills out of the ink tank 16, there is a possibility that the spilt ink will adhere to a slit provided to read movement of the ink jet head as an encoder signal. If the spilt ink adheres to the slit and disables the encoder so that it cannot read the movement of the ink jet head, the printing operation cannot be properly controlled. Further, if the spilt ink adheres to mechanical power transmitting parts (e.g., gears) or a supporting portion (e.g., a carriage shaft) for movably supporting the ink jet head, effective power transmission is blunted or the proper movement of the ink jet head is hindered by the adhering ink thus causing a malfunction or failure of the ink jet printer. Furthermore, while the user may move the ink jet printer some time after turning off the supply of the electric power, the user cannot actually determine whether the molten ink in the ink tank has solidified.